(US4966706-A)      Clarification sludge is treated, by (a) pretreating raw sludge contg. pathogenic germs, parasites, and germs for putrefaction with a (3C or less) peracid in concn. 500-6000 mg. per l. to destroy pathogens and parasites but not germs for digesting; and (b) digesting pretreated sludge.    Pref. peracid treatment takes place in a pre-concentrator, in a path between that and the digester, or immediately before the digester. Step (b) takes 8-20 days.    ADVANTAGE -   Sludge can be used as fertiliser contg. no offensive odours. (4pp)s    (DE3872324-G)      Sewage sludge esp. prim. and/or activated sludge, from waste water treatment, is treated with a 1-3C per-acid and allowed to rot in a putrifying lant.    Treatment with the per-acid may be in a preconcentrator, between the pre-concentrator and the utrifier, or just before the putrifier. Treatment is ref. with peracetic acid, in amt. of 5O0-6,000 mg/1 of sludge, for 1 mins.-2 h. Before feeding into the utrifier, the pH of the sludge may be brought to 7-9 by addn. of Ca0 or Ca(0H)2.    ADVANTAGE -   The sludge is sterilised and stabilised, and can be used as fertiliser, without great investment in plant, and with no redn. in gas (CH4) yield. The process is simple and rapid; residence time in the putrifying plant is 8-2 (1O-15) days, compared with 2O-25 days fro untreated sludge.    (JP2511116-B2)      Sewage sludge esp. prim. and/or activated sludge, from waste water treatment, is treated with a 1-3C per-acid and allowed to rot in a putrifying lant.    Treatment with the per-acid may be in a preconcentrator, between the pre-concentrator and the utrifier, or just before the putrifier. Treatment is ref. with peracetic acid, in amt. of 5O0-6,000 mg/1 of sludge, for 1 mins.-2 h. Before feeding into the utrifier, the pH of the sludge may be brought to 7-9 by addn. of Ca0 or Ca(0H)2.    ADVANTAGE -   The sludge is sterilised and stabilised, and can be used as fertiliser, without great investment in plant, and with no redn. in gas (CH4) yield. The process is simple and rapid; residence time in the putrifying plant is 8-2 (1O-15) days, compared with 2O-25 days fro untreated sludge.